Centrifugal extractor



CENTRIFUGAL EXTRACTOR 2 Sheets-Sheet 1 Filed 001:. 30, 1964 E w A M MEEQQQQ w INVENTORS Dana/d S. Webs/er Warren E. W/nsche Attorney y 6 D.s. WEBSTER ETAL 3,332,614

GENTRIFUGAL EXTRACTOR Filed Oct. 50, 1964 2 s-Sheet 2 III/1111111111INVENTORS Dana/d S. Webster Warren E Wmsc/re BY M 4. W

,dffomey United States Patent 3,332,614 CENTRIFUGAL EXTRACTOR Donald S.Webster, Aiken, S.C., and Warren E. Winsche, Bellport, N.Y., assignorsto the United States of America as represented by the United StatesAtomic Energy Commission Filed Oct. 30, 1964, Ser. No. 407,945 3 Claims.(Cl. 233-13) The invention described herein was made in the course of,or under, Contract AT(O7-2)1 with the US. Atomic Energy Commission.

The present invention relates to a centrifugal liquidliquid extractor.More particularly, this invention relates to an improved centrifugalextractor which provides remote regulation for continuous processing ofradioactive materials.

Liquid-liquid extractors, having a centrifugal pump mixer, integralcentrifugal separator and circular outlet weirs for the continuousseparation of liquids having different specific gravities from mixturesthereof have been described in Chemical Processing of Reactor Fuels,chapter VII, Academic Press, Inc., New York, 1961, page 271 and inChemical Engineering Practice, volume 6, by H. W. Cremer and T. Davies,Academic Press, Inc., New York, 1958, pp. 528-541. The theory andoperation of centrifugal separators generally is described in ChemicalEngineers Handbook 3rd edition, by J. H. Perry, McGraw- Hill BookCompany, Inc., New York, 1950, pages 992- 1001.

Where a solvent extraction process is used in the separation ofirradiated uranium, and other valuable nuclear materials, from lessvaluable or unwanted byproducts, it is known to use mixer-settlers.These devices mix aqueous and organic solutions for mass transfer, thenseparate the resulting dispersion by gravity in settling tanks. Largesettler volumes are needed to obtain complete separation of phases. Asubstantial reduction in the volume of the settler, and consequently inthe overall size, is achieved by using centrifugal force to aid settlingin devices known as centrifugal extractors and contactors. The smallervoltime requirement gives centrifugal contactors the advan tages ofreduced solvent and aqueous inventory, reduced space requirements,reduced exposure of solvent to radiation (when used to processradioactive fluids), and increased nuclear safety. In the centrifugalseparation of imiscible liquids, the heavy phase collects in the outerperipheral region within a rotating bowl and the light phase collectsnear the central region. For continuous operation, centrifugal,circular, weirs are provided for the heavy and light phases. The weirradii are chosen so that the interface between the liquid phases is atan intermediate radius which results in the heavy phase productcontaining a minimum amount of entrained light phase and the light phaseproduct containing a minimum amount of entrained heavy phase. Therequired weir heights are relatively independent of the absolute andrelative flow rates of the product streams. However, the Weir heightsrequired to maintain the interface at an intermediate radius varyappreciably with changes in the relative densities of the liquid phases.For some operations, such as liquid-liquid extractions of radioactivesolutions, it is highly desirable to provide quick acting remote controlof the interface position so that the centrifugal equipment canaccommodate changes in process conditions affecting relative densitiesof phases. Moreover, the equipment should be safe for processing nuclearmaterials and require minimum maintenance, and maximum reliability forcontinuous operation.

Accordingly, it is an object of the present invention to provide acentrifugal liquid-liquid extractor suitable for continuous processingof radioactive materials which may be regulated remotely.

It is a further object of the invention to provide a centrifugalextractor using circular weirs with a novel means for remotelycontrolling the interface between the liquid phases.

It is a still further object of the invention to provide such anextractor having maximum reliability under conditions of minimummaintenance, which is safe for use with nuclear materials, is efficientand has a high capacity and flexibility to cope with variations inliquid densities and flow rates.

The foregoing objects are accomplished by the present invention which isin a centrifugal liquid-liquid extractor comprising a cylindricalcentrifuge bowl, means to rotate said bowl about its cylindrical axis, amixing chamber at the lower end of said bowl, means for feeding processstreams into said mixing chamber, impeller means in said chamber formixing the process streams and pumping them into the bowl, outlets forthe heavy and light liquid phases, circular weirs in said bowl forcontrolling the flow of the heavy and light phases and forming a weirchamber, and means for applying air pressure on the liquid in the weirchamber for controlling the position of the interface between the liquidphases in the bowl.

Various other objects and advantages and the manner in which they may beaccomplished will be readily understood upon reading the followingdetailed description of the invention in conjunction with the attacheddrawings wherein:

FIG. 1 is a perspective view of a centrifugal extractor assemblyincorporating the invention, certain parts being cut away and shown incross-section for clarity; and

FIG. 2 is a schematic illustration of the weir section in the extractorof the invention.

Referring to FIG. 1, the centrifuge bowl, or rotor assembly, generallyindicated by 1 is rotatively mounted within a stationary housing orcasing 2. The rotor assembly is essentially a circular hollow cylindercomprising cylindrical bowl wall 3 having upper and lower end plates 4and 5, respectively, the upper end plate being connected at its centerby some conventional means 6 to a drive shaft 7. Drive shaft 7 is drivenby a vertically oriented induction motor, not shown, which is fixedlymounted to and supported by the top of the casing in a manner describedhereafter. The circular weir section and discharge ports are located inthe upper portion of the centrifuge bowl. The weir section comprises aplurality of spaced fiat, circular plates oriented perpendicular to therotational axis of the centrifuge which function to control the flows ofthe heavy and light phases leaving the bowl. In the embodiment hereinillustrated, the light phase weir is formed by a plate 8 having an ODsmaller than the ID. of the bowl wall 13 and which has circular opening9 at its center. A plurality of spaced radial ducts 10, formed integralwith or attached to the top of plate 8, communicate at their inner endssolely with opening 9 and at their outer ends solely withcircumferentially spaced outlet slots 11 through wall 3. The ducts 10are attached at their inner ends to shaft 7 and at their outer ends towall 3 by some suitable means, such as welding, for example, therebyforming circumferentially spaced openings 54 at the outer edge of plate8 for the passage of the heavy phase into the heavy phase weir chamberas will be described.

The heavy phase weir is formed by plate 12 attached at its outerperiphery to wall 3 and provided with circular opening at its center. Athird plate 13 which serves as a baffle is disposed in spacerelationship above plate 12 and is attached at its center to shaft 7.The outer radius of plate 13 is greater than the inner radius of plate12 but less than the radius of wall 3. A fourth plate 14, disposed inspace relationship between plate 13 and end plate 4, is attached at itsouter periphery to Wall 3, and is provided with an opening in its centerhaving a radius equal to that of the central opening in plate 12. Aplurality of circumferentially spaced outlet slots 15 are providedthrough wall 3 between plate 14 and end plate 4. Flat,

radial vanes 55 are provided between the circular plates 8, 12, 13 and14 to maintain constant angular velocity of the liquid in the weirsection.

The central portion of the bowl contains a plurality of radial vanes 16attached, as by welding, at their inner edges to shaft 7 and at theirouter edges to wall 3. The vanes extend the full length between plate 8and the lower end plate 5 thus forming pie shaped segments occupying themajor portion, called the settling section, of the centrifuge bowl.

Lower end plate 5 has central opening 17 which serves as an inlet forthe liquid mixture. Spaced above intake 17 is inlet diversion baflie 18which is formed by a circular plate attached at its inner circumferenceto the lower end of shaft 7 and having an outer radius greater than theradius of the bowl inlet 17. The purpose of the inlet diversion bafiieis to prevent injected solutions from spraying up the rotating assembly,thus partially bypassing some of the settling section. A plurality ofholes 19 are circumferentially spaced through the inlet diversion baflleto allow entrained air to pass directly to the air space in the settlingsection.

The rotating assembly is surrounded by a cylindrical casing 2 having aradially enlarged end section, opposite the weirsection of the bowl, inwhich is located the collection chambers for the light and heavy phases.The casing may be a generally welded construction as illustrated. Thecollection chambers are formed by outer cylindrical wall 20 having upperand lower flat annular end plates 21, 22 and intermediate flat annularplate 23. The inner diameters of plates 22 and 23 are slightly largerthan the outer diameter of centrifuge bowl 3 to provide clearance forfree rotation of the latter. Short cylindrical sections 24 and 25 areattached at their lower edges to the top inner edges of plates 22 and23, respectively, and extend upwardly therefrom to a position closelyadjacent to the lower edges of openings 11 and 15, respectively, in theupper end of wall 3. The lower inner edge of plate 23 is located closelyadjacent the top edges of slots 11. The uppermost annular chamber formedby this construction is the collection chamber for the heavy phase andthe lower annular chamber is for the light phase. Exit ports 26 and 27for the heavy and light phase chambers are provided through wall 20.Conventional connector means 28 and 29 for external conduits not shownare tangentially attached to wall 20 in communication with ports 26 and27. As illustrated, these are arranged for clockwise rotation of therotor.

Flanged motor mount 30 may be bolted as at 50 to the upper face of endplate 21. The induction motor not shown, which drives shaft 7 has itshousing attached to motor mount 30 in any convenient manner so that theentire rotor assembly is suspended from and supported solely by themotor and its bearings.

The lower end of casing 2 is flanged at 31 where it is connected tolower end plate 32, as by bolts 51, for example, a suitable sealinggasket 52 being inserted therebetween. End plate 32 contains a mixingchamber 33 formed by cylindrical section 34 and circular plate 35. Plate35 has a central opening 36 which is connected to T section 37 throughwhich the process liquids enter the separator. The radially innermostportion of the plate 32 has upwardly curved lip section 38 extendingthrough bowl inlet 17 in spaced relation therewith to provide for smoothflow of the mixture into the bowl and to minimize leakage of liquid intothe space between the bowl and casing.

The lower end of shaft 7 has attached thereto and coaxially therewithextension 39 passing through curved lip 38 into the mixing chamber wherethere is attached to its lower end a turbine blade assembly comprised ofdiametral flat blades 40 attached to the bottom of circular disk 53. Aflow direction baffle 41 is formed by a flat circular plate attached atits periphery to cylindrical section 34 in order to provide peripheralopenings. Baffie plate 41 has central hole 42 in spaced relationshipabout shaft extension 39 and has attached to its upper face a pluralityof radially extending antivortex vanes 47.

The drive shaft, centrifuge bowl assembly, casing assembly, inletdiversion baffie 18, bowl inlet 17, curved lip 38, baffle plate hole 42,shaft extension 39, and turbine blade assembly, are all coaxial, and allparts of the rotor assembly and weir section are geometrically uniform.A tangential drain connection 43 is provided between the casing and theinlet T to permit return of the liquid which collects in the spacebetween the centrifuge bowl and the casing.

Air pressure is supplied to the weir section by means of axial passage44 connected at its lower end to radial passages 45 through drive shaft7. The radial passages enter the weir section between plates 8 and 13.Air pressure from a source, not shown, is supplied to passage 44 througha rotary seal 46 at the upper end of the drive shaft.

The general operation of this centrifugal extractor will now bedescribed. The flow paths of the liquid phases are shown by the dashedand solid arrows which represent the light and heavy phasesrespectively. The drive motor through shaft 7 drives the rotor assemblyat the desired speed. The feed streams enter the mixing chamber throughT 37 and are mixed by turbine 40 which also pumps the dispersion, in thedirection of the arrows, through the peripheral openings in baffle plate41 and between the antivortex vanes 47 through inlet opening 17 into thecentrifuge bowl. Upon entering the bowl, the solution impinges upon theinlet dispersion baffle 18 and starts to travel towards the top of thebowl. Holes 19 in inlet diversion bafile allow air entrained within themixture to pass directly to the air space in the center of the settlingsection. The centrifugal force within the rotating bowl causes the heavyphase to settle rapidly from the dispersion toward the peripheral regionof the bowl. In turn the less-dense, light phase is displaced rapidlytoward the central region. As more clearly shown in FIG. 2, at the topof the bowl, the light phase flows over weir 8 through opening 9 intoradial ducts 10 where it is thrown outwardly through holes .11 into thelight phase collection chamber, from which it leaves the extractorthrough outlet means 29. v

The heavy phase is forced to the wall of the'bowl where it flows throughperipheral openings 54 and is forced radially inward between the lightphase radial ducts 10 and over the heavy phase weir at the centralopening of plate 12. It then flows under the bafiie plate 13, around theperipheral edge thereof, then radially inwardly under plate 14 and overthe inner edge thereof, fromwhere it is thrown outwardly through outlet15 into the heavy phase collection chamber, leaving through outlet means28.

The manner in which the air weir of the invention functions will bedescribed'with reference to the schematic illustration of FIG. 2 whichshows the upper portion of the centrifuge bowl assembly. In theliquid-liquid centrifugal extractor of this invention, during the timethe mixture is passing through the bowl the heavy H and light L phasesare continually separating producing therebetween an annular dispersionband, or interface. As flows are increased and residence time isdecreased, the width of the dispersion band inside the rotating bowlincreases until entrainment occurs in one or both of the end streams.Thus, the interface position has a critical effect upon the performanceof the extractor. The interface position in a centrifugal liquid-liquidseparator is a function of the radii of the outlet weirs for the lightand heavy phases and of the densities of the phases. In addition, forflow rates at which the crest of liquid over the weirs is appreciable,the interface position will vary with the flow rate. In this inventionair pressure is supplied through passages 44 and 45 to the heavy phaseweir chamber between plate members 8 and 13. The weir radii of plates 8and 12 are selected so that the interface radius is slightly less thanthe bowl radius when atmospheric pressure is applied to is now afunction of the air pressure in the heavy phase weir chamber, theposition of the dispersion can be adjusted by either increasing ordecreasing the air pressure until the end streams are free ofentrainment. The baflle plate 13 and weir plate 14 act as a seal for theair pressure applied to the heavy phase weir chamber.

The invention will be further illustrated by the following examples:

Example 1 A centrifugal liquid-liquid extractor of the design shown inFIG. 1 was fabricated of stainless steel. The centrifuge bowl 1 had anID. of inches and a length from the bowl inlet to the light phase outletweir of 10 inches. The pump and 'mixing chamber had a volume equal to10% of the volume of the bowl. The turbine pump impeller had four fiatblades one inch wide and six inches in diameter. The light phase weirradius was 2.0 inches and the heavy phase weir radius was 3.2 inches.

The machine was operated at 1800 rpm. and was fed an organic phasecomprising 30% tri-n-b-utyl phosphate dissolved in kerosene at 16g.p.m., and an aqueous phase "comprising 0.5 molar nitric acid at 24g.p.m. The specific gravities of the light and (heavy phases were 0.83and 1.01 respectively. The interface within the centrifuge bowl wasmaintained within the limits imposed by the internal and externaldiameters of the light phase weir (i.e., effective diameters of thelight phase weir and peripheral openings 54) by an air pressure of from4 to 9 p.s.i.g. applied to the heavy phase weir chamber. At an airpressure of 6 p.s.i.g. and for the above flow rates corresponding to ahold up time in the mixer and separator of about 10 seconds, theentrainment was less than 0.5% in either phase.

Example 2 In this example the apparatus and procedure of Example 1 wasduplicated, except that uranyl nitrate was added to the aqueous phase tomake a solution containing 10 grams of uranium per liter of solution.The efliciency of extraction of uranium by the organic phase was greaterthan for a holdup time of 10 seconds, and greater than for a holdup timeof 20 seconds, compared to the separation obtained during agitated batchcontacting of the same solutions for 20 minutes.

It is not intended that this invention be limited to the specificembodiments described and illustrated in the foregoing specification butonly by the scope of the appended claims.

Having thus described our invention, we claim:

1. A centrifugal liquid-liquid extractor comprising a cylindricalcentrifuge bowl mounted in a housing for rotation about its cylindricalaxis, means at one end of said bowl for feeding process liquids intosaid bowl, a weir section comprising a plurality of spaced apart flatcircular plates extending generally perpendicular to the rotational axisof said bowl at the other end, the first of said plates having centraland peripheral openings of respective passage of light and heavy phaseliquid therethrough, at least one duct positioned to communicate at itsone end with said central opening and at its other end with a lightphase outlet from said bowl, a second of said plates having a peripheralopening at a radius greater than said central opening of said secondplate, said first and third plates defining a heavy phase weir chamber,means in said bowl for introducing pressurized gas in said weir chamberfrom an external source, a heavy phase outlet from said bowl beyond saidthird plate, and means positioned between said third plate and saidheavy phase outlet for cooperating with said third plate to seal saidpressurized gas in said weir chamber.

2. The centrifugal liquid-liquid extractor of claim 1 wherein said meanspositioned between said third plate and said heavy phase outlet is aflat circular plate having a central opening having a radius less thansaid radius of said peripheral opening of said third plate.

3. The centrifugal liquid-liquid extractor of claim 1 wherein said ductpositioned to communicate with said central opening of said first plateand said light phase outlet from said bowl is substantially radial.

References Cited UNITED STATES PATENTS 703,630 7/1902 Ten Winkel 23321736,976 8/1903 Keiper 23328 1,247,473 11/1917 Weston 233-21 2,083,8096/1937 Asch 233-28 3,081,027 3/1963 COulson 23314 X M. CARY NELSON,Primary Examiner.

H. T. KLINKSIEK, Assistant Examiner.

1. A CENTRIFUGAL LIQUID-LIQUID EXTRACTOR COMPRISING A CYLINDRICALCENTRIFUGE BOWL MOUNTED IN A HOUSING FOR ROTATION ABOUT ITS CYLINDRICALAXIS, MEANS AT ONE END OF SAID BOWL FOR FEEDING PROCESS LIQUIDS INTOSAID BOWL, A WEIR SECTION COMPRISING A PLURALITY OF SPACED APART FLATCIRCULAR PLATES EXTENDING GENERALLY PERPENDICULAR TO THE ROTATIONAL AXISOF SAID BOWL AT THE OTHER END, THE FIRST OF SAID PLATES HAVING CENTRALAND PERIPHERAL OPENINGS OF RESPECTIVE PASSAGE OF LIGHT AND HEAVY PHASELIQUID THERETHROUGH, AT LEAST ONE DUCT POSITIONED TO COMMUNICATE AT ITSONE END WITH SAID CENTRAL OPENING AND AT ITS OTHER END WITH A LIGHTPHASE OUTLET FROM SAID BOWL, A SECOND OF SAID PLATES HAVING A PERIPHERALOPENING AT A RADIUS GREATER THAN SAID CENTRAL OPENING OF SAID SECONDPLATE, SAID FIRST AND THIRD PLATES DEFINING A HEAVY PHASE WEIR CHAMBER,MEANS IN